This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-227937, filed Aug. 11, 1999; and No. 11-227938, filed Aug. 11, 1999, the entire contents of which are incorporated herein by reference.
Conventionally, when LEI parts are assembled on a flexible printed circuit (FPC) substrate, a COB (chip on board) method has been mainly used, wherein an IC bear chip 10 is located on a FPC substrate 20 with an electrode 11 thereof upward, the chip electrode 11 and a FPC substrate electrode 21 are wire-bonded with each other by means of an Au wire 30, and subsequently the whole body is sealed by means of a resin 31, as shown in the cross-sectional view of FIG. 6.
On the other hand, recently a bump connection method such as BGA (ball grid array), CSP (chip sized package), flip chip and the like having an electrode on the lower side thereof has been increasingly employed. FIG. 7 is a cross-sectional view showing an example thereof. The bear chip 10 is located on the lower surface with the electrode 11 downward, and is connected with the electrode 21 of the FPC substrate 20 with a bump 32 such as a ball or the like therebetween.
In a flip chip assembly method, since the substrate electrodes 21 must be opposed to each other in the same pitch as the IC electrode 11, it is indispensable to form a fine pattern. However, when a double-sided (two-layer) type substrate is used as the FPC substrate 20, and a chip is assembled on a front surface (upper layer) circuit pattern, an uneven rear surface (lower layer) circuit pattern influences also the front surface circuit. Therefore, it is usual to make the rear surface circuit portion on the chip assembly part a solid pattern land by means of the widest Cu circuit possible. However, it is difficult in design to bypass such an extremely wide solid pattern circuit portion and to draw out a fine pattern.
Moreover, in order to prevent short circuit between the electrodes, a solder resist is used around the connection portion between the chip and the circuit pattern in the chip assembly part, and due to a fine pattern this raises difficult problems in the production process including the selection of a resist material and the discussion of an applying method.
Moreover, in the flip chip assembly, the rear surface of the IC chip 10 looks upward and is exposed in the highly heat-insulating air, what is disadvantageous with respect to the radiating characteristics. Therefore, conventionally a radiating part such as a radiating fin or the like is bonded on the rear surface of the IC chip 10 by means of a heat-conductive adhesive in order to improve the radiation property. However, the method of bonding a radiating part on the chip causes the deformation or destruction of the assembly part due to a mechanical stress applied to the chip itself and to the assembly part on the lower surface thereof by the gravity of the radiating part.
In a COB method shown in FIG. 6, wire bonding is possible at any position where a wire loop of the Au wire 30 can be formed. So, the signal line from the LSI pad and the power source and ground lines can be connected separately to the substrate side so that the electric characteristics of the assembly module may become advantageous.
FIG. 8 is a cross-sectional view showing an example thereof. There are two kinds of substrates used in this chip assembly module, and the one is a single-sided FPC substrate 20 applied to the output side drawing out a signal line in a fine pitch. The other is a double-sided RPC substrate 40 applied to the input side requiring a power source line and a ground line to be drawn in a thick pattern. The single-sided FPC substrate 20 is fabricated by integrating upper and lower two-layer insulating films 23 and 24 with a conductive circuit pattern 22 therebetween. RPC double-sided substrate 40 is fabricated by forming upper and lower two-layer conductive patterns 41 and 42 in an insulating board 43. These substrates 20 and 40 are bonded at a bonding part 33.
In a bump connection method shown in FIG. 7, the substrate electrodes must be also opposed to each other in the same order as in bump array (LSI pad array), and an equal pitch pattern must be formed on the substrate. However, there are difficulties in realizing this. Particularly, in the flip chip assembly, it is difficult to form a fine pattern and to isolate a signal line, a power source line and a ground line from each other. In a COB assembly structure shown in FIG. 8, there are no such problems, however, this structure can not be applied to the bump connection method requiring a flat chip assembly pat. Moreover, by using the RPC double-sided substrate 40, there is an increase in cost.
Therefore, one object of the present invention is to provide a chip assembly module of bump connection type being capable of being made thin as a whole and also being capable of radiating heat efficiently from the assembled chip.
Another object of the present invention is to provide a chip assembly module of bump connection type having superior electric characteristics and being capable of performing a high density assembly by using only a FPC double-sided substrate.
According to the present invention, a chip assembly module is provided, comprising:
a multi-layer structured printed circuit substrate having at least an upper conductive layer and a lower conductive layer with an inter-layer insulating layer and having a chip assembly part formed thereon;
a chip having a bump part formed therein which is assembled in the chip assembly part of the printed circuit substrate by means of bump connection method; and
a flat plate type radiating plate located on the printed circuit substrate, wherein
the chip assembly part is formed by forming a chip opening corresponding to the chip on the upper conductive layer, forming a bump opening corresponding to the bump part of the chip on the inter-layer insulating layer exposed from this chip opening, and exposing the lower conductive layer from this opening, and the chip is buried in the chip opening of the chip assembly part and assembled so that the upper surface thereof may protrude from the upper conductive layer;
the radiating plate has substantially the same opening as the chip opening of the chip assembly part, and it also has such a thickness as the upper surface thereof is only a little higher than the upper surface of the chip assembled in the chip assembly part; and
a heat conductive adhesive is filled between the inner wall of the opening of the radiating plate and the side of the chip.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.